Clinical trial design – an easy-to-understand overview

If you’re unfamiliar with clinical trial design, you’re not alone. Many health writers who don’t have a medical or scientific background find this aspect tricky.

Even experienced writers who are used to reading journal articles can forget what the study design involves!

Here’s an overview of clinical trial design – sometimes also referred to as clinical study design.

We take a look at experimental, observational, analytical and descriptive studies.

Understanding clinical trial design

As a health writer, you rely on evidence-based research to support your writing. Whether your audience are consumers or medical specialists, you should ensure you’re providing your readers with quality content. This includes all types of health writing – from health copywriting to health blogging and medical writing.

Interpreting medical evidence goes beyond reading the abstract of a study. You should always access the fully published study to understand medical research and clinical trial design. Most importantly, do this to critically analyse the evidence.

Understanding the research can also help to boost the credibility of your writing. There is nothing worse than sensationalising the findings from a study or misrepresenting new evidence. It not only damages the quality of the original medical research but can also harm your reputation as a health writer.

Experimental studies in clinical trial design

Experimental studies answer the “why” or “how” questions. Experimental studies measure the relationship between two factors where the effect of a test, treatment, procedure or program is introduced to observe an outcome:

• Randomised controlled trial (RCT). Considered the most powerful tool in evidence-based medicine, an RCT is a quantitative study where participants are allocated in random to receive one of several clinical interventions to compare and obtain a measurable outcome,
• Blinded RCT. These trials offer evidence without bias, as participants and trial investigators are unaware who is receiving treatment. Non-blinded trials are called “open” or “unblinded”.
• Clustered RCT. Participants are randomised to intervention or control in groups such as, families, communities or hospitals.
• Controlled clinical trial (CCT). Similar to a RCT but the participants are not randomly assigned to a treatment or control group.

Observational clinical trials

When defining clinical trial design, think of research questions: “what is” or “what was”.

Researchers ask questions from participants to observe the effect of a risk factor, diagnostic test or treatment. This is done to collect information on prevalence, incidence or experience (such as data collection using existing medical records).

Sometimes an observational study is conducted before an experimental study to gain insight before testing a hypothesis.

Analytical clinical trials

• Cohort study. Researchers observe one group of similar participants exposed to a particular variable in comparison to another group who aren’t exposed.
• Prospective study. A cohort study following participants over time.
• Retrospective cohort. The data collected for the study is based on events that have already happened.
• Case-control study. Participants who have a condition/disease (case) are compared to participants without (control), to obtain information about previous exposure to the treatment or intervention being studied.
• Interrupted time series study. Measures a sample or series of samples from the same population obtained several times before and after a manipulated or a naturally occurring event.

Descriptive

• Case reports. Sometimes containing a literature review of similar cases, a report contains a medical profile of a patient based on rare, unexpected or unique findings.
• Case series. A single group of participants are exposed to the treatment or intervention.
• Surveys (cross-sectional studies). One-time interaction with groups of people.
• Ecological study. Study of risk modifying factors on health within a population defined geographically o temporally.
• Longitudinal study. A study that follows participants over time.

But wait, there’s more

There’s more than just clinical trial design to consider when you’re critically analysing medical research.

• Journal’s impact factor (IF). The IF refers to a measure of frequency an average article published in the journal is cited within a year. Journals with a higher IF are considered better ranking than lower ones.
• Evidence is published in one of the top ranking journals (includes NEJM, The Lancet or JAMA)
• Study has a large number of participants.
• Evidence is recent and published within the last five years.
• The hierarchy of evidence. The most reliable evidence comes from systematic reviews, meta-analyses or Cochrane reviews. This is followed by evidence from RCTs, cohort studies and then case-control studies.

Have you got any tips or useful ideas to remember different clinical trial designs? Share your thoughts in the comments below.